Effect of season on the metabolizable energy requirement for broiler growth, carcass yield and carcass composition

Two experiments were conducted at The University of Tennessee, Knoxville, poultry farm to evaluate effects of high and low ambient temperatures on the metabolizable energy requirement for broiler growth, carcass quality and carcass composition. The first experiment was conducted in July through September, while the second experiment was conducted in December through February, as these two seasons represent the two temperature extremes prevalent in the southeastern part of the United States.

Both experiments employed a 23% crude protein corn soybean diet with the following dietary energy levels: 2880, 3040, 3200, 3360 and 3520 kcal ME/kg diet. Diets were fed to color-sexable Shaver chicks from 1 day of age until an average treatment live body weight of 2.05 kg was achieved.

In experiment 1, a total of 330 day-old color-sexable chicks were utilized. Eleven male and eleven female chicks were randomly allotted to each experimental group. Results obtained indicated a linear response of both gain and feed efficiency to dietary energy level at 28 and 49 days of age. Abdominal fat pad expressed as percentage of live weight increased in males and females as dietary energy level increased. Abdominal fat pad increased in females approximately 8.42% for every 5% increase in metabolizable energy, and 36.04% for every 5%, or more specifically, 160 kcal ME/kg diet in males.

In experiment 2, increasing dietary energy level improved (P < .0001) feed efficiency. Both dietary energy level and sex significantly (P < .0001) affected live weight gain. Abdominal fat pad weight was also significantly affected by dietary energy level (P < .0001) and by sex (P < .0001). Chickens fed the low energy diets contained approximately 57% less abdominal fat content than those fed high energy diets. Females contained an average of 20% more abdominal fat than males.

Season had a marked effect on broiler performance. For example, it required 57 days for birds fed the 2880 kcal ME/kg diet to achieve an average live weight of 2.05 kg during the summer, but only 49 days during the winter. In general, these results indicate that 3200 kcal ME/kg diet is adequate during both summer and winter seasons. Although higher dietary energy levels resulted in heavier body weights, the high cost of these high fat diets would probably make such a feeding system not feasible.